A gas turbine engine extracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. In its simplest form, a gas turbine engine has an air compressor (radial, axial, or centrifugal flow) fluidly coupled to a turbine with a combustion chamber disposed therebetween. Energy is released and work is performed when compressed air is mixed with fuel and ignited in the combustor, directed over the turbine's blades, spinning the turbine. Energy is extracted in the form of shaft power (e.g., turboshaft engines) and/or compressed air and thrust (e.g., turbojet/turbofan engines).
Compressors generally include a compressor wheel with a plurality of spaced apart blades or vanes on that wheel. The compressor wheel is rotated about an axis within the engine housing to receive air from an inlet, accelerate and compress that air, and then discharge the air through an outlet. To be most efficient, the air is generally forced to flow between the space defined by the blades, the rotational hub of the compressor wheel and a portion of the engine housing commonly referred to as a compressor case. The case also includes blades or vanes in staggered orientation to the wheel vanes to further compress the air.
Compressor efficiency is often greatest when a minimal running clearance is maintained between the case and the tips of the wheel blades or vanes to prevent leakage of the air around the tip of the blades. However, during normal operation of the compressor, centrifugal forces acting on the compressor wheel cause it to “grow” radially in the direction of the case. Thus, establishing minimum running clearance at operational speeds of the compressor can be a complex task given the variables involved. An error in case position could result in a significant loss of operating efficiency or cause damage to the compressor when the blades bind against the case. For instance, the blades may fracture and be consumed by the engine, causing engine failure. Blades or vanes coming into contact with the compressor case may also cause sparks that could cause the entire engine to ignite, creating an explosion.
Therefore, the addition of a lining or coating has been included within compressor cases. The coating is a thin layer, usually a plastic and resin mixture, that minimizes clearance between the coating and the tips of the wheel vanes. Additionally, the coating or lining is made to be abradable, which allows the vanes to extend into the coating if they expand due to the centrifugal forces, or other reasons. The spinning vanes can contact the lining without the possibility of the vanes being damaged, or of sparks or ignition occurring.
However, problems exist with the compressor case plastic lining. For instance, many of the gas turbine engines are used with aircraft, such as airplanes and helicopters. In use, the engines may cycle between extreme low and high temperatures from start-up to shutdown. The number of cycles is important, as many repairs and/or inspections are required at engine or device specific cycle levels. As the number of cycles, and thus, the use of the device increases, there is a greater chance for things to fail. Because of the composition of the plastic liners currently used in compressor cases, the higher the number of thermal cycles causes the lining to become damaged. The cycling of extreme high and low temperatures can produce cracks in the plastic lining. If the lining is not repaired or replaced during one of the inspections, pieces of the lining could become detached and strike the vanes or other engine components, creating damage. The damage to the compressor vanes would decrease the efficiency of the engine. If the damage is great enough, it could cause the engine to fail.
Therefore, at appropriate time and cycle levels, the compressor case lining is inspected for cracks. If they exist beyond acceptable limits, the cracked lining must be removed, and the compressor case repaired and overhauled with a new lining for safe use in an engine. However, the cost of replacing a compressor case with a repaired and overhauled case is high. Having liners that crack at lower time and cycle levels make owning and operating aircraft incorporating the compressors expensive.
Therefore, there is a need in the art for an improved compressor case lining for use with a gas turbine engine that creates a minimal running clearance, but that is also abradable. There is also a need for an improved compressor case lining that has a longer cycle life than plastic liners.
It is therefore a primary object, feature, and/or advantage of the present invention to overcome or improve on deficiencies in the art.
It is another object, feature, and/or advantage of the present invention to provide an improved compressor case lining that is stronger than the prior art.
It is another object, feature, and/or advantage of the present invention to provide an improved compressor case lining that last more cycles.
It is another object, feature, and/or advantage of the present invention to provide a compressor case that is repaired and overhauled with a new lining.
It is yet another object, feature, and/or advantage of the present invention to provide a compressor case lining using a carbon fiber mixture.
It is still a further object, feature, and/or advantage of the present invention to provide a compressor case lining that is abradable and will not damage compressor vanes.
It is yet another object, feature, and/or advantage of the present invention to provide an improved compressor case lining including multiple layers for both strength and to meet industry standards.
These and/or other objects, features, and advantages of the present invention will be apparent to those skilled in the art. The present invention is not to be limited to or by these objects, features and advantages. No single embodiment need provide each and every object, feature, or advantage.